No compromise on rules?

I have 3 dc aged 5 and under. When I say it's bedtime I mean it's BEDTIME. I may change the time they go to bed depending on when they are tired but once i say its time to go then no amount of moaning will make me change my mind. What rule do you not ever compromise on?Or AIBU?

My DDs know that they can put their argument to me and I will listen but it's rare that I change my mind. For that reason they don't usually bother.

If you have as few rules as possible you don't need to compromise on them often which means the children feel secure because they know where they stand.

One thing I always come down on hard is asking one parent when the other has already said no. That is a big bugbear of mine and when I see friends' children do it I find it very hard to bite my tongue. Mine are always worse off for trying that one so they learned very quickly not to do it.